The present invention relates to a surface treated product that moves relatively in a fluid.
A technique of improving a flow state of a fluid is known such as providing dimples on a surface of an object on which a fluid flows to reduce resistance of the fluid. It is well known that a golf ball with dimples provides a long carry, and such a technique is disclosed in several patent documents.
For example, Japanese Patent Laid-Open No. 11-304300 (Patent document 1) proposes an efficient and noiseless refrigeration cycle in which a plurality of dimples are formed on a surface of a part through which a coolant passes. Japanese Patent Laid-Open No. 8-247343 (Patent document 2) discloses a heat exchanger tube in which many dimples are provided on an inner peripheral surface to improve heat transfer efficiency. Japanese Patent Laid-Open No. 10-28314 (Patent document 3) discloses a pipe type jumper apparatus in which dimples are formed on a surface to reduce air resistance and reduce rolling caused by wind pressure loads. Further, Japanese Patent Laid-Open No. 11-190471 (Patent document 6) proposes a pipe with low pipe line resistance in which pipe line resistance is reduced for use as a horizontal pipe line, and Japanese Patent Laid-Open No. 2000-55014 (Patent document 7) proposes a fluid resistance reducing apparatus in which dimples are arranged orderly to significantly reduce fluid resistance.
The applicant of the present invention proposes an intake pipe for an engine in which a wall surface of an intake passage is uneven with many small protrusions and recesses in Japanese Patent Laid-Open No. 5-149204 (Patent document 4), and proposes an exhaust pipe for an engine in which a wall surface of an exhaust passage is uneven with many small protrusions and recesses in Japanese Patent Laid-Open No. 5-149132 (Patent document 5), and achieves certain advantages.